Chapter 28 - SadavaPlants without Seeds: from Water to Land

Before we start Plants, a review…. Domain Archaea

Prokaryotic, include extremophile bacteria Domain Bacteria

Prokaryotic, includes what we knew as Kingdom Monera

Domain Eukarya Eukaryotic Includes:

Kingdom Fungi What we knew as Kingdom Protista (green algae

are related to plants) Kingdom Plantae Kingdom Animalia

Land plants are monophyletic all descend from a single

common ancestor One shared derived character

a synapomorphy development from an embryo

protected by tissues of the parent plant Why is this important on land?

Also called embryophytes

Land plants retain derived features they share with green algae (which are protists): Chlorophyll a and b. Starch as a storage product. Cellulose in cell walls.

Photo 28.2 Green algae of phylum Chlorophyta are most likely ancestors of plants.

“Plants” can be defined in several ways Streptophytes include land plants and a

paraphyletic group of green algae —all retain egg within parent’s body

Green plants: streptophytes plus all other green algae. All have chlorophyll b

This textbook: “plants” refers only to land plants

What we think of in Kingdom Plantae

10 clades of land plants

Vascular plants, or tracheophytes 7 clades all have conducting cells called

tracheids

The seven groups of vascular plants constitute a clade themselves

Nonvascular plants 3 clades

www.sonoma.edu/users/c/cannon/

Plants first appeared on land between 400–500 million years ago

Adaptations were needed to survive in dry environments Large plants must transport water to all

parts of plant Needed support in air Needed methods to disperse gametes

Characteristics of land plants: The cuticle (waxy lipids) Stomata – openings in stems and leaves;

regulate gas exchange (except liverworts) Gametangia enclosing gametes Embryos in a protective structure Pigments that protect against UV radiation Spore walls containing sporopollenin Mutualistic relationships with fungi to

promote nutrient uptake from soil

Alternation of generations

All land plants have a life cycle with alternation of generations

multicellular haploid (gametophyte)

multicellular diploid (sporophyte) individuals

Alternation of generations Sporophyte

Produces spores, all cells are diploid Cells in sporangia (in sporophyte)

undergo meiosis to produce haploid, unicellular spores

Spores are released Spore develops into multicellular haploid

structure, the gametophyte Gametophyte

Produces gametes, all cells are haploid Produce gametes by mitosis Fusion of egg and sperm results in

diploid zygote Zygote develops into sporophyte

Reduction of the gametophyte generation is a major theme in plant evolution In nonvascular plants: gametophyte is

larger, longer-lived, and more self-sufficient than the sporophyte

Gametophyte is photosynthetic

In plants that appeared later, this is reversed In seed vascular plants (gymnosperms

and angiosperms), sporophyte generation is dominate

Sporophyte is photosynthetic Gametophyte might only be a few cells it is so

small

Nonvascular plants Do not have vascular tissue liverworts, hornworts, and mosses These groups do not form a clade – why?

In nonvascular plants, the gametophyte generation is photosynthetic Sporophytes may or

may not be photosynthetic,…

but are always nutritionally dependent on gametophyte, and is permanently attached

http://taggart.glg.msu.edu/bot335/MOSS.GIF

Gametophytes

Sporophytes arising from gametophytes

Haploid gametophyte produces gametes in specialized sex organs (gametangia) Female: archegonium produces one

egg Male: antheridium produces many

sperm with two flagella each

http://www.dkimages.com/discover/previews/832/20113674.JPG

Flagellated moss sperm Archegonium Antheridium

• Nonvascular plants• Sperm must swim to

archegonium, or be splashed by raindrops

• Egg or archegonium releases chemical attractants for sperm

• Water is required for all these events

Vascular Plants• Vascular plants include the club mosses,

ferns, conifers, and angiosperms (flowering plants).

• True roots and leaves

What Features Distinguish the Vascular Plants?

The vascular system consists of tissue specialized for transport of materials Xylem

conducts water and minerals from soil up to aerial parts of plant.

Some cells have lignin — provides support

Phloem conducts products of photosynthesis

through plant.

http://plantandsoil.unl.edu/croptechnology2005/UserFiles/Image/siteImages/Fig-3-large.gif

Tracheids are main water-conducting element in xylem

Evolution of tracheids in plants set stage for invasion of land

First plant fossils are from Silurian (408-440 mya) Made land more

hospitable for animals Amphibians and insects

arrived soon after plants

www.unlv.edu/Colleges/Sciences/Biology/Schulte/Anatomy/CellsTissues

Vascular plants also have a large, branching, independent sporophyte Mature sporophyte is

nutritionally independent from gametophyte

http://web.cortland.edu/broyles/hayghttp://virtual.yosemite.cc.ca.us/randerson/Lynn's%20Bioslides/20.jpg

Small independent gametophyte (left) and branched sporopythe (right) of ferns

Fern prothallus

• Vascular plants• Euphyllophytes• “true leaf plants”• Includes:• Monilophytes – seedless vascular plants that have

megaphylls • seed plants (gymnosperms and flowering plants)

• Synapomorphies include overtopping growth — new branches grow beyond the others —an advantage in the competition for light

True leaves evolved flattened photosynthetic structures

arising from a stem or branch has true vascular tissue two types

Microphylls – small, one vascular strand Club mosses have these

Megaphylls

Heterosporous vascular plants produce two types of spores: Megaspores develop into female

gametophytes — megagametophyte Megaspores are produced in small

numbers in megasporangia Microspores develop into male

gametophytes — microgametophyte Microspores are produced in large

numbers in microsporangia

Nonvascular seedless land plants: three clades: liverworts mosses hornworts

EmbryophytesNonvascular Seedless plantsHepatophyta

Liverworts: Hepatophyta Sporophytes very short

Remember that gametophyte generation is dominant in nonvascular plants

Can reproduce asexually Do so by dispersing gemmae which are in

gemmae cups

www.bcbiodiversity.homestead.com/files

EmbryophytesNonvascular Seedless plantsBryophyta

The mosses: Bryophyta Mosses (plus hornworts and vascular

plants) have stomata important in water & gas exchange

EmbryophytesNonvascular Seedless plantsAnthocerophyta

Hornworts: Anthocerophyta Gametophytes are flat plates of cells Have stomata, which do not close

http://www.botany.org/PlantImages/Conant/CA06-014_300.jpg

Seedless Vascular Plants

Seedless VASCULAR plants – three monophyletic clades: club mosses horsetails whisk ferns

plus ferns and allies (not monophyletic, though 97% are)

Seedless Vascular Plants

Seedless vascular plants Small, short-lived

gametophyte is independent of the large sporophyte

Single-celled spore is resting stage

Can grow larger because of vascular tissue but must have water for part of life cycle — for the flagellated, swimming spermwww.biologie.uni-hamburg.de/b-online/library/webb/BOT311/FERNS

EmbryophytesSeedless Vascular PlantsLycophytes

Lycophytes: club mosses, spike mosses, and quillworts Roots and stems have dichotomous

branching Leaves are microphylls Strobilli – clusters of sporangia

Lycopodium annotinum

http://ip30.eti.uva.nl/bis/flora/pictures

EmbryophytesSeedless VascularEuphyllophytesMonilophytes

Monilophytes (a.k.a. Pteridophytes) — horsetails, whisk ferns, and ferns & allies, form a clade Horsetails and whisk ferns are both

monophyletic, but ferns are not But 97% of ferns form a clade — the

leptosporangiate ferns

EmbryophytesSeedless VascularEuphyllophytesMonilophytes

Horsetails 15 species in one

genus — Equisetum Silica in cell walls —

“scouring rushes”… used for cleaning

www.plantoftheweek.org/image

Equisetum hymale

EmbryophytesSeedless VascularEuphyllophytesMonilophytes

Whisk ferns 15 species in two

genera No roots but

well-developed vascular system

http://www.botanik.uni-karlsruhe.de/garten/fotos-knoch/Psilotum%20nudum%20Gabelblatt%201.jpg

Psilotum nudum

EmbryophytesSeedless VascularEuphyllophytesMonilophytes

Sporangia occur on undersides of leaves in clusters called sori

http://departments.bloomu.edu/biology/pics/botany/fern_sori2w.jpg

Monilophytes (Pteridophytes) – Ferns

Fern gametophytes produce antheridia and archegonia, not always at same time or on same gametophyte

www.esu.edu/~milewski/intro_biol_two/lab_2_moss_ferns

EmbryophytesSeedless VascularEuphyllophytesMonilophytes

Most ferns found in shaded, moist environments Tree ferns can reach heights of 20 m

http://www.we-du.com/images/plants/350/frndrydwf.jpg

Dixie Woods fern, Dryopteris australis

Tree fernshttp://www.wettropics.gov.au/st/rainforest_explorer/Resources/Images/plants/TreeFerns.jpg